Roberto T. Leon Virginia Polytechnic Institute and State University Blacksburg, Virginia Sponsors: National Science Foundation American Institute of Steel Construction Georgia Institute of Technology University of Illinois at Urbana- Champaign Seismic Performance Factors for Steel-Concrete Composite Frame Structures Quake Summit 2012 Boston, Massachusetts July 12, 2012 Mark D. Denavit University of Illinois at Urbana-Champaign Urbana, Illinois Jerome F. Hajjar Northeastern University Boston, Massachusetts
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Roberto T. Leon Virginia Polytechnic Institute and State University Blacksburg, Virginia
Seismic Performance Factors for Steel-Concrete Composite Frame Structures. Mark D. Denavit University of Illinois at Urbana-Champaign Urbana, Illinois Jerome F. Hajjar Northeastern University Boston, Massachusetts . Roberto T. Leon Virginia Polytechnic Institute and State University - PowerPoint PPT Presentation
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Roberto T. LeonVirginia Polytechnic Institute and State University
Blacksburg, Virginia
Sponsors: National Science FoundationAmerican Institute of Steel ConstructionGeorgia Institute of TechnologyUniversity of Illinois at Urbana-Champaign
Seismic Performance Factors for Steel-Concrete Composite
Frame Structures
Quake Summit 2012Boston, Massachusetts
July 12, 2012
Mark D. DenavitUniversity of Illinois at Urbana-Champaign
Urbana, Illinois
Jerome F. HajjarNortheastern UniversityBoston, Massachusetts
Seismic Performance Factors for Composite Frames
• NEESR-II: System Behavior Factors for Composite and Mixed Structural Systems
• FEMA P695 - Quantification of Building Seismic Performance Factors
• Two seismic force resisting systems as defined in the AISC Seismic Specification– Composite Special Moment Frames (C-
SMF)– Composite Special Concentrically Braced
Frames (C-SCBF)
System o R CdC-SMF 3.0 8.0 5.5C-SCBF 2.0 5.0 4.5
Steel Girders
Composite Column
Selection and Design of Archetype Frames
= Location of Braced Frame= Fully Restrained Connections
High 20’ Dmax 4 ksi 1 a a a a a aHigh 20’ Dmax 12 ksi 2 a a aHigh 20’ Dmin 4 ksi 3 a a a a a aHigh 20’ Dmin 12 ksi 4 a a aHigh 30’ Dmax 4 ksi 5 a a a aHigh 30’ Dmax 12 ksi 6 a aHigh 30’ Dmin 4 ksi 7 a a a aHigh 30’ Dmin 12 ksi 8 a aLow 20’ Dmax 4 ksi 9 a a a a a aLow 20’ Dmax 12 ksi 10 a a aLow 20’ Dmin 4 ksi 11 a a a a a aLow 20’ Dmin 12 ksi 12 a a aLow 30’ Dmax 4 ksi 13 a a a aLow 30’ Dmax 12 ksi 14 a aLow 30’ Dmin 4 ksi 15 a a a aLow 30’ Dmin 12 ksi 16 a a
Mixed Beam-Column Element
• Mixed formulation with both displacement and force shape functions
• Total-Lagrangian corotational formulation
• Distributed plasticity fiber formulation: stress and strain modeled explicitly at each fiber of cross section
Archetype frames are categorized into performance groups based on basic structural characteristics
Group Number
Design Gravity Load
Level
Design Seismic Load
LevelPeriod
DomainNumber of
C-SMFsNumber of
C-SCBFs
PG-1 High Dmax Short 6 4
PG-2 High Dmax Long 2 2
PG-3 High Dmin Short 6 4
PG-4 High Dmin Long 2 2
PG-5 Low Dmax Short 6 4
PG-6 Low Dmax Long 2 2
PG-7 Low Dmin Short 6 4
PG-8 Low Dmin Long 2 2
System Overstrength Factor, Ωo
• By the FEMA P695 methodology, Ωo should be taken as the largest average value of Ω from any performance group– Rounded to nearest 0.5– Upper limits of 1.5R and 3.0
• High overstrength for C-SMFs– Displacement controlled design– Current value (Ωo = 3.0) is upper limit and is
acceptable• Overstrength for C-SCBFs near current
value (Ωo = 2.0)– Higher for PG-3 and PG-4 (High gravity load,
SDC Dmin)
Group Number
Average Ω
C-SMF C-SCBF
PG-1 5.8 1.9
PG-2 5.2 1.9
PG-3 7.8 3.2
PG-4 11.7 2.6
PG-5 5.8 1.6
PG-6 5.8 1.7
PG-7 7.11 2.2
PG-8 7.59 2.0
By the FEMA P695 methodology, the R factor assumed in the design of the frames is acceptable if:• the probability of collapse for
maximum considered earthquake ground motions is less than 20% for each frame
• and less than 10% on average across a performance group.
Parameter Expression
Collapse margin ratio
Spectral shape factor
Adjusted collapse margin ratio
Total system collapse uncertainty
Acceptable value of ACMR
Response Modification Factor, R
System Quality of Design Requirements Quality of Test Data Quality of Nonlinear
ModelingTotal System Collapse Uncertainty for μT ≥ 3
C-SMF B (Good)DR = 0.2
B (Good) TD = 0.2
B (Good) MDL = 0.2 total = 0.525
C-SCBF B (Good) DR = 0.2
B (Good) TD = 0.2
B (Good) MDL = 0.2 total = 0.525
20%iACMR ACMR
( 10%mean iACMR ACMR
ACMR SSF CMR
ˆCT MTCMR S S
( , , )TSSF f T SDC
( % ,X totalACMR f X
2 2 2 2total RTR DR TD MDL
Response Modification Factor, R
• ACMR10% = 1.96 for both C-SMF and C-SCBF
• ACMR values show correlation with the overstrength
• C-SMFs– Current value (R = 8.0) is acceptable
• C-SCBFs– Current value (R = 5.0) is acceptable
Group Number
ACMR
C-SMF C-SCBF
PG-1 4.58 3.32
PG-2 3.06 2.77
PG-3 7.33 5.20
PG-4 8.37 5.41
PG-5 4.95 2.65
PG-6 4.27 2.09
PG-7 7.81 4.07
PG-8 9.29 4.35
Deflection Amplification Factor, Cd
• By the FEMA P695 methodology, Cd = R for these systems• Would represent a minor change for C-SCBF
– Current values: Cd = 4.5, R = 5.0– Typically strength controlled design
• Would represent a significant change for C-SMF– Current values: Cd = 5.5, R = 8.0– Typically displacement controlled design
• Four C-SMF archetype frames designed with the current Cd value – Lower overstrength with current Cd
– Acceptable performance with current Cd
Conclusions
• Steel-concrete composite frames shown to exhibit excellent seismic behavior
• Current seismic performance factors for C-SMF and C-SCBF found to be acceptable
• Further investigation of the need for and effects of setting Cd equal to R is warranted for C-SMF